1. Field of the Invention
The present invention relates to a method and an apparatus for wastewater treatment using activated sludge, and more particularly to a method and an apparatus for an advanced treatment in which the floatation separation and concentration of sludge using the micro-bubbles generated upward is an alternative to the conventional secondary clarifier and can be combined with an existing nitrogen/phosphorous removal process to effectively remove organic substances, nitrogen, phosphorous, suspended solids and the like of the waste water. The present invention also relates to a method and an apparatus for wastewater treatment in which an electrode plate generating the micro-bubbles is made of Al or Fe so that phosphorous can be coagulated and removed by Al or Fe ions.
2. Description of the Prior Art
In a biological wastewater treatment process that removes organic substances, nitrogen, phosphorous, and the like from wastewater, the microorganisms called activated sludge are the biological solid matter that performs the most significant function. The operation efficiency of a wastewater treatment process using activated sludge (an activated sludge process) is much affected by high pollutants and hydraulic load including the concentration and the state of activated sludge in a reactor vessel, hydraulic retention time, solids retention time, and the like. In particular, the concentration of activated sludge is considered as a very important operation factor in an advanced wastewater treatment process including nitrogen/phosphorous removal as well as the conventional activated sludge process. However, the gravity settling that is the most universal solid-liquid separation method to separate sludge from the treated wastewater cannot regulate the concentration of the activated sludge in the reactor vessel in proper or maintain it in high concentration. In particular, it is indicated that a sludge bulking generated intermittently and a sludge re-floatation by nitrogen gas occurring via denitrification in a clarifier, and the resulting decrease in efficiency of solid-liquid separation and the excessive loss of the activated sludge are the problems that are the most difficult to solve with the gravity settling.
As methods that have been developed for operation of high concentration activated sludge process, there are an activated sludge process using a membrane bioreactor (MBR), a pure oxygen aerated process, a bio filter process using a carrier that is a representative bed attached growth process, and so on. However, in case of MBR process or bio filter process, incipient expenses for the purchase of membrane or carrier are large and, after a long-term operation, the blocking occurs due to the activated sludge or sludge secretion, causing the pressure loss to be increased. Accordingly, it has a problem in that a periodic washing or backwashing should be performed. In case of pure oxygen aerated process, since the excellent settling of sludge should be continuously secured in order to maintain the activated sludge in high concentration, it is known that stable operation thereof is impossible and it is also difficult for the concentration of the microorganisms in an aeration vessel to be maintained above 8,000 mg/L. Further, it also has a defect in that additional expenses are taken to supply pure oxygen.
Beside these methods, a sequencing batch reactor (SBR) process has been developed and adapted to the wastewater treatment wherein the unit steps of fill, reaction, settle, draw of wastewater, and idle are continuously performed in a single reactor vessel according to an array of predetermined time. This method is very advantageous with respect to stable management of wastewater or the like in that a secondary settling tank is not required because the respective unit steps are performed in a single reactor vessel, that it is easy to control filamentous fungi, and that it is easy to fabricate. However, the SBR process has a drawback in that it cannot maintain the concentration of mixed liquor suspended solids (MLSS) high to a desired level and a cycle time of overall process must be increased because a time taken for settling reaction that may be substantially essential is long. Moreover, the existing SBR process has a problem in that in case where a feature of water flow in the reactor vessel is changed in the process of discharging the processed water, the sludge particles are swept away by discharged water.
Meanwhile, in view of low C/N ratio and C/P ratio of domestic wastewater by nature, it is practically difficult to simultaneously remove nitrogen and phosphorous. Accordingly, it has been studied a method that nitrogen is removed biologically, and phosphorous is removed physically and chemically. However, most of phosphorous removal technologies studied or developed have had drawbacks of additional expenses due to addition of chemicals and instability of process efficiency due to intermittent injection of chemicals.